1. Field of the Invention
This invention relates generally to organic light emitting diodes (OLEDs) and more particularly to a method of making a stacked, non-inverted, dielectrically isolated, organic light emitting diode display using a silicon-on-insulator (SOI) based active matrix backplane.
2. Description of the Related Art
The present invention is an OLED display, which uniquely utilizes a SOI substrate in place of a conventional silicon substrate for allowing the stacked OLEDs to be driven in reverse and thus conveying both positive and negative voltage through the bulk.
An OLED device typically includes a stack of thin layers formed on a substrate. A light-emitting layer of a luminescent organic solid, as well as adjacent semiconductor layers, are sandwiched between a cathode and an anode. The light-emitting layer may be selected from any of a multitude of fluorescent and phosphorescent organic solids. Any of the layers, and particularly the light-emitting layer, also referred to herein as the emissive layer or the organic emissive layer, may consist of multiple sublayers.
The SOI substrate, or silicon wafer herein also referred to as a backplane, is unique in that the silicon junction is above the electrical insulator.
In an OLED device, one or more layers of semiconducting organic material are sandwiched between two electrodes. An electric current is applied across the device, causing negatively charged electrons to move into the organic material(s) from the cathode. Positive charges, typically referred to as holes, move in from the anode. The positive and negative charges meet in the center layers (i.e., the semiconducting organic material), combine, and produce photons. The wave-length—and consequently the color—of the photons depends on the electronic properties of the organic material in which the photons are generated. In the present invention, the presence of SOI technology allows the electric current to move in reverse, or from a plus to a minus range and vice versa.
Prior art OLED display technology utilizes an active matrix backplane using conventional silicon technology with the limited option of conveying only positive voltage through the bulk. While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.
The OLED display of the present invention utilizes a new OLED architecture with multiple units stacked in sequence with intermediate electrodes electrically connected through vias.
A “via’ is a vertical electrical connection between different layers of conductors in a physical electronic circuit. Vias have been described in detail and their use disclosed in a plurality of prior art patents. Specifically, U.S. Patent Publication Nos. 2004/0207315, 2005/0236981, 2010/0295443, and U.S. Pat. Nos. 7,384,816, and 6,885,157 disclose the use of vias in OLED technology. In particular, paragraph [0052] of publication 2004/0207315, describes vias in use with OLED display devices.
In the present invention, electrical connections to and from OLED displays are provided to each anode line and cathode line by a plurality of vias. Each via is formed of a column of conductive material or in its simplest form provided as an opening leaving free access to the electrode beneath.
The proposed stacked OLED of the present invention requires application of a voltage that is both positive and negative with respect to the control node. This is not physically possible with conventional bulk silicon technology because the active transistor devices in bulk silicon process are electrically isolated using reverse bias depletion junctions. These junctions are all tied to a common voltage at zero volts. Driving a transistor negative with respect to a common substrate potential would forward bias these junctions and render the transistors inoperative. In order to overcome this limitation, a technology with dielectrically isolated transistors is required. Such a technology may be comprised of a thin film transistor material on a glass substrate such as used in large active area displays or a SOI technology as shown and described herein.
It is, therefore, a primary object of the present invention to provide a display and method of making a display comprising a stacked, non-inverted, dielectrically isolated organic light emitting diode formed on a SOI substrate.
It is, therefore, a primary object of the present invention to provide a display and method of making a display comprising a stacked, non-inverted, dielectrically isolated organic light emitting diode formed on a thin film transistor material on a glass substrate.
It is another object of the present invention to allow voltage across an OLED stack to be both positive and negative and thus allow the OLEDs to be driven in reverse.
It is another object of the present invention to provide a method that can be implanted in any type of active matrix OLED display.
It is another object of the present invention to provide a method for use in a micro-display that will allow for the reduction of pixel dimensions and enhancement of resolution.